How Can You Tell if a Reindeer Is Pregnant?

In a snowy valley on the island of Spitsbergen, 500 miles north of mainland Norway, a reindeer is getting a pregnancy test.

She's lying in the snow, grumpily. One leg has been popped out of the hobble that ties her other three legs together, and she has already used it to kick snow on me, the ultrasound machine, and veterinarian Erik Ropstad, who chuckles.

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Spitsbergen is the largest island in the archipelago of Svalbard—no, it wasn't invented for the children's fantasy book The Golden Compass; it's a real place, with real polar bears. I spent a week there this time last year to report on a long-term study on reindeer for Smithsonian magazine.

Every spring since 1995, a few British and Norwegian scientists have been going to Svalbard to chase reindeer. They stay in a tiny cabin on the edge of vast, white Reindalen—Reindeer Valley. There's no running water but plenty of beer, box wine, and Scotch.

Each day they go out on snowmobiles to look for reindeer they've tagged in past years. They use binoculars to pick out an animal with collar and ear tags, usually high up on a hillside, send a snowmobile or two to herd it down to flat land, then chase it with a big net.

The idea is to understand how the numbers of reindeer change over the years—are there more? Fewer? What causes the ups and downs? They tag only females; if you want to understand how a group of animals is expanding and contracting, you really need to know about fertility.

Thus the pregnancy test.

Ropstad pulls the bottle of ultrasound gel out of his snowmobile suit where it has been staying warm against his body—reindeer don't like cold gel on their skin any more than humans do—and squeezes it on the probe, then holds the end of the probe to her nipple, the only piece of bare skin on a reindeer. Conveniently, it's right next to the uterus.

With bright white snow below, bright white mountains on either side, and bright white sky overhead, the screen looks like a solid piece of black glass. The solution to this problem is low-tech: an old blue sleeping bag to cover Ropstad's head and the screen so he can see the images. I join him under there.

There's a lot of stuff gurgling and swishing inside a reindeer's belly, so it takes an experienced eye to pick out a moving fetus among them. “The baby,” he says, pointing out its beating heart with one hand as he moves the probe with the other. I'll take his word for it—as far as I'm concerned, it could be a bit of rippling gut or an errant vole. "Pregnant, live!" he calls to the guy writing down the numbers on a data sheet.

The scientists' analysis suggests that what really harms Svalbard reindeer, in this changing world, is rain in winter. It dribbles through the snow and freezes on the ground like Magic Shell on a bowl of ice cream. Except it doesn't taste like chocolate and it can be inches thick, too much for the animals to paw through to get at the vegetation below. In bad years, animals go hungry and few are pregnant. It had been a good winter for the reindeer; not much rain fell. Nearly every female deer they caught that week was fat and pregnant.

This week the scientists are out chasing the reindeer again, for the 20th time, to find out how they made it through this year's warm, sometimes rainy winter. While North America was getting blasted by the polar vortex this winter, Northern Europe was freakishly warm. As the scientists chase down reindeer and look at their innards this week, they'll be finding out if fewer adorable baby reindeer will be joining the population this summer.

Helen Fields is a freelance science writer in Washington, D.C. She writes about whales, meteorites, poop, and whatever else comes to mind. Follow her on Twitter.